<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Display</title>
    <link rel="stylesheet" href="./style.css">
    <style>
        /* 块级元素 */
        /* 行内元素 */
        /* 行内块级元素 */
        
    </style>
</head>
<body>
    <div class="flex">
        <ul class="flex-items">
            <li class="item" data-key="item_1">1</li>
            <li class="item" data-key="item_2">2</li>
            <li class="item" data-key="item_3">3</li>
        </ul>
    </div>
</body>
</html>